Place a large skillet over medium heat and add pancetta. Sauté pancetta until golden, remove the pancetta with a slotted spoon, and drain on a paper towel.

Add 1 tbsp olive oil to the drippings in the pan. If pancetta doesn't produce much in the way of drippings, use 2 tbsp olive oil. Add garlic and jalapeño chiles. Sauté for 1 minute. Add the fennel to the skillet and cook until the fennel begins to soften, about 5 minutes. Stir in chicken broth, 2 tbsp finely chopped fresh Italian parsley, lemon juice, and crushed fennel seeds. Bring the mixture to a boil, then reduce the heat to low, cover the skillet, and cook until the fennel is very tender, 20 to 30 minutes. Remove the skillet from the heat and season with salt and pepper.

Bring a large pot of salted water to a boil over high heat. Add 1 pound (16 oz.) spaghetti and cook until al dente. Before draining the pasta, scoop out and reserve 1 cup of the pasta cooking water. Drain pasta and return it to the pot.

Place the skillet with the fennel mixture over high heat, remove the lid, and cook until most of the liquid is absorbed, 4 to 5 minutes. Pour the fennel mixture over the pasta. Add 2 tablespoons olive oil, 3/4 cup finely grated Parmesan cheese, and pancetta. Toss the pasta and add the pasta cooking water, 1/4 cup at a time, if the pasta needs more moisture. Season with salt and pepper. Transfer pasta to serving bowl, sprinkle with 2 tablespoons chopped fresh Italian parsley, and serve with additional grated Parmesan cheese.